Alum-Cs2CO3 as a new recyclable solid base catalyst for the efficient syntheses of arylidenemalononitriles, esters and arylcinnamic acids in water

Article abstract of DOI:10.14233/ajchem.2014.15569

The condensation between aromatic aldehydes and malononitrile, ethylcyanoacetate and malonic acid for the syntheses of arylidenemalononitriles, arylidenemalonic acid esters and aryl cinnamic acids in water using alum-Cs₂CO₃ as a solid support catalyst has been described. Alum-Cs₂CO₃ was found to be a highly active, stable and recyclable catalyst under reaction conditions.

Full text of DOI:10.14233/ajchem.2014.15569

Asian Journal of Chemistry; Vol. 26, No. 7 (2014), 1938-1942
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.15569
Alum-Cs2CO3 as a New Recyclable Solid Base Catalyst for the Efficient Syntheses of
Arylidenemalononitriles, Esters and Arylcinnamic Acids in Water
*
ASHOK KUMAR TADURI and B. RAMA DEVI
Department of Chemistry, Jawaharlal Nehru Technological University Hyderabad, College of Engineering, Kukatpally, Hyderabad-500 085, India
*Corresponding author: Email: ashok.jntu@gmail.com
Received: 3 April 2013;
Accepted: 8 October 2013;
Published online: 22 March 2014;
AJC-14931
The condensation between aromatic aldehydes and malononitrile, ethylcyanoacetate and malonic acid for the syntheses of
arylidenemalononitriles, arylidenemalonic acid esters and aryl cinnamic acids in water using alum-Cs2CO3 as a solid support catalyst has
been described. Alum-Cs2CO3 was found to be a highly active, stable and recyclable catalyst under reaction conditions.
Keywords: Alum-Cs2CO3, Arylidenemalononitriles, Arylidene malonic acid esters, Aryl cinnamic acids, Water, Green approach.
which were useful intermediates for many pharmaceutical and
biomedical industries.Arylidenemalononitriles were primarily
used in the preparation of fine chemicals in agriculture and
medicine fields as precursors of heterocycles with biological
activity11. Whilst arylidene derivatives of ethylcyanoacetate
were successfully employed in the synthesis of cyanocou-
marins12, as antimetabolites13. Moreover, cinnamic acid
derivatives have major applications in many fields such as in
medicine as anticancer14, antituberculosis agents15 and in
industries as plasticizers, perfumes and aroma compounds16
and as lubricants etc. There is a wide range of catalysts other
than metal and solid supports were used for Knovenagel
condensation like modified hydrotalcites17, amines18, K2CO319,
Lewis-acid catalysts20 and ionic liquids21.
INTRODUCTION
Since Green chemistry is primarily concerned with the
reduction of chemical hazards and pollution1. The use of environ-
ment friendly reagents and solvents in organic synthesis will
be beneficial for both industry as well as for environment.
Thus, the use of water as solvent in chemical reactions has
proved to be a cleaner and safer alternative to organic solvents2.
Heterogeneous catalysis, which has the rapid and imp-
roved advantage of easy recoverability and recyclability and
sometimes has further advantages of increased selectivity of
the desired product over traditional homogeneous catalysis, is
a key process in organic syntheses.
Various types of heterogeneous solid support catalysts
have been employed so far. Recently, alum3 has been proved
as an efficient catalyst for Knovenagel condensation due to its
promising ability for C-C bond formation reactions4. Alum
was also earlier used for the synthesis of various pharma-
ceutical intermediates like dihydropyrano[3,2-b]chromene-
diones5, arylidene-2,4-thiazolidinediones6, substituted couma-
rins3, pyrano[2,3-d]pyrimidinone and tetrahydrobenzo[b]pyran
derivatives7, bis(indolyl)methanes8 and also used for variety
organic transformations such as Biginelli9 and Pechmann3
reactions. Various other catalysts were also employed for
Knovenagel reactions like AlPO4-Al2O3, ZnCl2, LiBr, CdI,
K3PO4, Fe2(SO3)4, TiCl3(SO3CF3), FeCl3, InCl3, RuCl3 and
lanthanum triflates10.
The Knovenagel condensation is strongly solvent depen-
dant22,23. In addition, the use of aqueous and highly protic
solvents is currently of great importance since it avoids problems
of self-condensation, 1,2-elimination and retro-Knovenagel
reactions.
Herein, we report facile preparation of alum supported
cesium carbonate (alum-Cs2CO3) and its effective application
to the Knovenagel condensation between different aromatic
aldehydes and ethylcyanoacetate or malononitrile or malonic
acid by stirring in water at 80-100 °C and also by using
microwave irradiation technique. The products were obtained
in high yield and purity.
EXPERIMENTAL
It was found that solid support catalysts like alum were
found active when they treated with Cs2CO3. Without doubt,
an alternative strategy for Knovenagel reaction by this
approach is worthwhile since it produces series compounds
All melting points are uncorrected and were obtained
using open capillary tubes in sulfuric acid bath. TLC analysis
was carried out on glass plates coated with silica gel-G and

Vol. 26, No. 7 (2014)
Efficient Syntheses of Arylidenemalononitriles, Esters and Arylcinnamic Acids in Water 1939
spots were visualized using iodine or a UV lamp. IR spectra
were recorded using Perkin-Elmer Model 46 instrument in
General procedure for microwave method using alum-
Cs2CO3: To a mixture of aldehyde (1 mmol), malononitrile or
ethylcyanoacetate or malonic acid (1 mmol), alum-Cs2CO3 (0.5
g) and distilled water (5 mL) in a 10 mL CEM-reaction tube
sealed by rubber stopper and subjected to microwave
irradiation for 5 min at 100 °C in the commercial micro-wave
reactor. After that, the tube was cooled and the completion of
reaction was checked by TLC. The reaction mixture was diluted
with ethylacetate and alum-Cs2CO3 was filtered off. The organic
layer was separated and dried over anhydrous Na2SO4. The
product was obtained after removal of the solvent under reduced
pressure and recrystallized from ethanol. The catalyst was
washed with distilled water (20 mL) and followed by ethyl
acetate (15 mL) and dried 1 h at 100 °C for further use. The
1
KBr discs. H NMR were recorded in CDCl3/DMSO using
400 MHz Varian Gemini spectrometer and mass spectra were
recorded on LC-MS spectrometer, model HP-5989A. TGA
was recorded on Perkin Elmer Pyris DiamondThermalAnalyzer
in the temperature range 0-600 °C, with a heating rate of 10
K/s. XRD spectra from the ECA pressed samples were
recorded by a rotating anode X-ray diffractometer (Rigaku 12
kW) with Cu-Kα radiation and a graphite monochromator,
operating at 50 kV and 150 mA.
Preparation of alum supported cesium carbonate
(alum-Cs2CO3): To a mixture of alum (3 g) and Cs2CO3 (2.92
g) were grinded in a mortar using pestle for 10-15 min and the
resulting compound washed with distilled water (10-15 mL).
The reaction mixture was filtered, dried overnight at 100 °C
and later at heating at 600-700 °C in a muffle furnace for 1 h.
General procedure for synthesis of arylidenemalono-
nitriles, arylidenemalonic acid esters and aryl cinnamic
acids using alum-Cs2CO3: To a mixture of aldehyde (1 mmol),
malononitrile or ethylcyano acetate or malonic acid (1 mmol)
and distilled water (10 mL) in a round-bottom flask (50 mL),
alum-Cs2CO3 (0.5 g) was added. The reaction mixture was
allowed to heat on water bath at 100 °C for appropriate time
(Table-1) with shaking regularly. The completion of the reaction
was monitored by TLC. The reaction mixture was diluted with
ethyl acetate and alum-Cs2CO3 was filtered off. The organic
layer was separated and dried over anhydrous Na2SO4. The
product was obtained after removal of the solvent under
reduced pressure and recrystallized from ethanol. The catalyst
was washed with distilled water (20 mL) and followed by ethyl
acetate (15 mL) and dried 1 h at 100 °C for further use. The
1
structures of the products were confirmed by IR, H NMR,
mass spectral data and comparison with authentic samples
RESULTS AND DISCUSSION
Alum is an inexpensive, non-toxic, commercially available
which is easily hand-able without any precautions. Equivalent
amounts of alum and Cs2CO3 were grinded in a mortar using a
pestle for 15-30 min and washed it with double distilled water.
The filtered solid was allowed to dry over night at 100 °C and
later at 600-700 °C in a muffle furnace for 1 h. The characteri-
zation of alum-Cs2CO3 was done by TG-DTA, FTIR and X-
ray diffraction analysis.
TG-DTA analysis of alum-Cs2CO3:The TG-DTA analysis
of alum-Cs2CO3 indicates that the material is degraded in five
discrete steps mainly as shown in Fig. 1. The initial three degra-
dations from 90-480 °C indicates the weight loss due to loss
of moisture/or crystallization of water in three stages24 (30-
50 %) and the fourth effect with the dissociation of KAl(SO4)2
and the formation of K2SO4·Al2O324. The fifth degradation at
630 °C indicates mass loss related to Cs. This weight loss can
1
structures of the products were confirmed by IR, H NMR,
mass spectral data and comparison with authentic samples.
TABLE-1
ALUM-Cs2CO3 CATALYZED KNOVENAGEL CONDENSATION OF AROMATIC ALDEHYDES WITH MALONONITRILE
AND ETHYLCYANOACETATE AT 80-100 °C AND IN m.w. METHOD AT 450 W FOR 3-5 min IN WATER
S.
No.
Time (min)
At 100 °C
Yield (%)b
At 100 °C
Producta Ar = 3(a-q)
X
m.p. (Lit. m.p) °C [Ref]
m.w.
5
m.w.
98
96
90
90
94
90
90
92
90
90
94
90
90
94
90
92
90
1.
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
120
150
120
180
120
180
150
180
180
180
180
180
150
150
120
120
120
96
94
90
94
92
88
88
90
90
96
94
94
92
90
86
88
90
83-84 (82-83) Ref. [26]
160-161(161) Ref. [26]
77-78(77) Ref. [26]
3a –C6H5
2.
5
3b 4-OCH3-C6H4
3c 4-Cl-C6H4
3d 4-OH-C6H4
3e 3-NO2-C6H4
3f 3-OCH3-C6H4
3g 2-OH-C6H4
3h 2-thiophenyl
3i 2-Furyl
3.
4
4.
4
135-136(134-135) Ref. [ 26]
160(159-160) Ref. [26]
128-130(128) Ref. [26]
73-74(74) Ref. [26]
5.
5
6.
5
7.
3
8.
5
103-104(104) Ref. [26]
72-73(72) Ref. [10]
9.
4
10.
11.
12.
13.
14.
15.
16.
17.
5
126-127(126-129) Ref. [26]
49-50(49-52) Ref. [26]
89-90(90-94) Ref. [26]
87-88(88-90) Ref. [26]
128-130(129-132) Ref. [26]
91-92(90-92) Ref. [26]
112-114(114-115) Ref. [26]
94-95(94) Ref. [10]
3j –CH=CH-C6H5
3k –C6H5
COOEt
COOEt
COOEt
COOEt
COOEt
COOEt
COOEt
5
5
3l 4-Cl-C6H4
4
3m 4-OH-C6H4
3n 3-NO2-C6H4
3o 4-CH3-C6H4
3p –CH=CH-C6H4
3q 2-Furyl
4
4
5
5
aAll the products were characterized by 1H NMR, IR and mass spectral data and comparison with the authentic samples available commercially or
prepared according to the reported methods.
bYields refers to the isolated yields.

1940 Taduri et al.
Asian J. Chem.
104
102
100
98
8000
6000
(480°C)
Alum-Cs2CO3
(92°C)
4000
2000
0
(280°C)
96
-2000
-4000
-6000
(640°C)
700
94
92
100
200
300
400
Temperature (°C)
500
600
Fig. 1. TG-DTA of alum-Cs2CO3
20
30
40
50
(°)
60
70
80
be related to the release of carbon dioxide due to the precipi-
tation of CO32-. There is a complete degradation after 700 °C
is due to SO42- in nitrogen atmosphere. The TGA data indicated
the high stability of alum-Cs2CO3 up to 700 °C (Fig. 1).
The FTIR of alum-Cs2CO3 has showed a weak absorbance
at 1610 cm-1 due to CO32- and the tetrahedral SO42- ion showed
four bending vibrations at 981, 451, 1104 and 613 cm-1, respec-
tively25.
2
θ
Alum-Cs2CO3
X-ray diffraction analysis: The X-ray diffraction analysis
of alum-Cs2CO3 indicates the crystalline nature of the catalyst.
The diffractograms at different 2θ values indicates the presence
of different mineral oxides present in the alum-Cs2CO3. The
X-ray analysis is interpreted by comparing with commercial
alum data which indicates the modified structure of alum-
Cs2CO3. This data showed that, alum-Cs2CO3 when heated at
high temperature, it is destroyed into K2SO4·Al2O3 which were
represented by inter planar spacing values (2θ). The 2θ value
at 3.6525 and 3.2471 indicates the presence of modified
crystalline K2SO4 and α-Al2O324. The 2θ value at 3.1228 related
to cesium carbonate which was modified into fine hexagonal
crystalline Cs2O, which was absent in commercial alum X-
ray data is a strong evident for successful catalyst preparation.
The remaining diffractograms indicates the fine grained
crystalline form of alum-Cs2CO3 (Fig. 2).
Commercial alum
20
30
40
50
(°)
60
70
80
2
θ
Fig. 2. X-Ray diffractograms of alum-Cs2CO3 and comparison with
commercial alum
distilled water was investigated. In order to optimize the
reaction conditions, the condensation between malonic acid
and p-chloro benzaldehyde was carried out with respect to
different molar ratios of alum-Cs2CO3, temperature, substrates
and solvent.
The Knovenagel condensation between aromatic alde-
hydes and malononitrile or ethylcyanoacetate or malonic acid
in the presence of catalyst alum-Cs2CO3 independently in double
TABLE-2
SYNTHESIS OF ARYLCINNAMIC ACIDS 4(a-h) USING MALONIC ACID AND ALDEHYDES
Time (min)
Yield (%)b
At 100 °C At 100 °C
Producta Ar = (4a-h)
S. No.
m.p (Lit. m.p) °C
m.w.
m.w.
96
1
2
3
4
5
6
7
8
240
180
180
240
180
210
240
240
5
4
4
5
4
5
5
5
94
92
90
82
88
80
86
85
136-137 (135-136)
245-247 (248)
4a (C6H5)
94
4b (C6H4-p-Cl)
90
210-211 (209-210)
197-198 (196-198)
>250 (285)
4c (C6H4-p-F)
84
4d (C6H4-p-CH3)
90
4e (C6H4-p-NO2)
86
242-244(243)
4f (Piperonaldehyde)
4g (Furfuraldehyde)
4h (Thiopene-2-aldehyde)
90
142-144(139-141)[50]
14-145 (145)[50]
90
aAll the products were characterized by 1H NMR, IR and mass spectral data and comparison with the authentic samples available commercially or
prepared according to the reported methods.
bYields refers to the isolated yields.

Vol. 26, No. 7 (2014)
Efficient Syntheses of Arylidenemalononitriles, Esters and Arylcinnamic Acids in Water 1941
p-Chlorobenzaldehyde and malonic acid were taken as
sample test compounds. It was found that no reaction occurred
between p-chlorobenzaldehyde and malonic acid in water at
100 °C. The same reaction was carried out with alum indepen-
dently. After 12 h TLC indicated that the reaction had pro-
ceeded very slightly and, after workup, the product was isolated
in only 2-5 % yield. Similar results obtained when the reaction
was repeated with Cs2CO3 (reaction time 24 h) and gave the
isolated product in 5 % yield. As a consequence, when we
carried out the reaction with alum-Cs2CO3, the amount of the
catalytic systems needed was optimized with sample test
substrates and with 0.2-0.6 g of the catalyst. It was found that
0.5 g of catalyst gave optimum results in terms of reaction
time and yield (Table-2).
Cs2CO3 was thoroughly washed again with ethyl acetate and
dried at 100 °C for overnight. This was be used for subsequent
five fresh batches for the Knovenagel condensation. It has been
observed that the efficiency of the catalyst reducing little as
the number times that it recovered from the reaction mixture.
It also influencing on the reaction time and yield (Table-3,
Fig. 3).
TABLE-3
RECOVERABILITY AND REUSABILITY OF
ALUM-Cs2CO3 FOR THE SYNTHESIS OF 3
S. No.
No. of the batches
Time (min)
Yield (%)
1
2
3
4
5
6
1st batch
2nd batch
3rd batch
4th batch
5th batch
6th batch
180
180
180
180
180
180
90
90
85
75
60
50
Secondly, the reaction with the test substrates was carried
out at different temperatures (40, 60, 80 and 100 °C) and 100 °C
was found to be the optimum reaction temperature. The same
set of reactions were carried out in CEM-discovered microwave
synthesizer at 450 W for 3-5 min and has got good results. A
comparative study was carried out with K2CO3 and CaCO3.
These appear to be good catalysts but suffer from the
disadvantages of low reaction rate and poor solubility in water.
The amount of water as solvent was optimized with 5-10 mL
of distilled water and it was found that 10 mL of water was
sufficient to carry out the reaction in an efficient, mild and cost-
effective way. Thus, the optimum conditions were established
as: aldehyde (1 mmol), malonic acid (1 mmol), alum-Cs2CO3
(0.5 g) and water (10 mL) at an optimum temperature of 100
°C and in microwave conditions at 450 W for 3-5 min. Under
these conditions, product 4 (Table-2) was obtained in 96 %
isolated yield after 2 h. This methodology was also applicable
to heteroaromatic aldehydes and unsaturated aldehydes (3h,
3i, 3q & 3j, 3p Table-1). Promising better yields were obtained
in 92, 90, 90 and 90, 92 % yields after 2-3 h respectively
(Schemes I and II).
100
90
80
70
60
50
40
30
20
10
0
No. times recovered
Yield (%)
1
2
3
4
5
100
90
80
70
60
50
40
30
20
10
0
CN
X
CN
alum-Cs2CO3
Reflux, Water
Ar
C
H
Ar-CHO
X
(1)
(2)
(3)
No. times recovered
Yield (%)
alum-Cs2CO3
Water, M.W, 450 W, 3-5 min
X = CN, COOEt
Scheme-I
COOH
COOH
Alum-Cs2CO3
Reflux, Water
H
C
Ar
C
H
Ar-CHO
COOH
1
2
3
4
5
(1)
(4)
Fig. 3. Recoverability of alum-Cs2O3 and yield of 3(b) graphical interpre-
tation
Alum-Cs2CO3
Water, M.W, 450 W, 3-5 min
Scheme-II
Conclusion
Recoverability and reusability of the catalyst (alum-
Cs2CO3): To demonstrate the recyclability and reusability of
alum-Cs2CO3, an intimate mixture of aldehyde (1 mmol),
malonic acid (1 mmol) and alum-Cs2CO3 (0.5 g) in water were
refluxed at 100 °C about 3 h and after the completion of the
reaction, ethyl acetate was added to the reaction mixture and
the catalyst was recovered by filtration. The recovered alum-
An efficient Knovenagel condensations were achieved
between a range of aromatic aldehydes and malonic acids or
malononitriles or ethylcyanoacetates in short time periods by
using alum-Cs2CO3 as the catalyst and water as solvent under
mild conditions both at refluxing temperature and microwave
method. Due to its reusability, these catalysts are very efficient
for C-C bond forming reactions.

1942 Taduri et al.
ACKNOWLEDGEMENTS
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Hyderabad for providing laboratory facilities and also grateful
for CSIR-CDRI, Lucknow for providing financial support.
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